Tincture of iodine as acid pickling inhibitor



United States Patent TINCTURE-OF IODINE AS AGID 'PICKLING INHIBITOR Karl F. Hager, Huntsville, Ala. ;Morris Rosenthal, Alexandria, Va., assignors to the United States of America as represented by the Secretary of the Army No Drawing. Application March 5,1952,

Serial 'No. 274,677 6 Claims. (Cl. 252147) improved inhibitor for acid pickling. Other objects of the invention will be evident hereinafter.

Dilute non-oxidizing acids such as sulfuric, hydro chloric, phosphoric, acetic, formic and the like are com monly used in pickling and metal cleaning operations. For such acids many inhibitors are known, including the halides upon which the present inventors are filing herewith companion patent applications Serial Number 274,675 and 274,676. It is also well known, however, that ethanol increases the rate of attack of pickling acids against the base metals.

We have discovered that, contrary to expectation, even a 2% solution of iodine in ethanol added in small amounts to a pickling acid is an eifective inhibitor. In fact, this solution is a much more effective inhibitor than the iodine disclosed alone in the companion cases. For example 0.1% of a 2% tincture of iodine in a nonoxidizing pickling acd, a total of 0.002% iodine content, is a better inhibitor than 0.002% pure iodine dissolved in the same acid. By tincture of iodine we mean the ordinary product available on the market which contains about 7% iodine, potassium iodide and 5% water made up to 100% with ethyl alcohol, in accordance with the definition given in standard reference works.

Ethanol and iodine evidently exert a synergistic influence on each other. As a result of this joint influence the inhibiting properties of iodine are enhanced and the tendency of ethanol to increase the rate of attack of the etching acid is completely overcome. The synergistic effect can clearly be seen from the following examples.

Example 1.-Pieces of SAE 1010 steel were pickled in beakers containing 5% sulfuric acid, about 1 N. Two pieces were treated in acid containing no inhibitor and were utilized as controls in both this and the following examples. A third-piece of the steel was pickled in 5% sulfuric acid to which 0.002% iodine had been added. A fourth piece was pickled in 5% sulfuric acid containing 0.1% of a 2% tincture or a total iodine content of 0.002%.

Weight loss determinations may be made directly or, since the hydrogen evolved is proportional to the iron dissolved, by determination of the volume of hydrogen produced. The latter method was followed in this case with the results given in Table 1. All experiments were run without stirring at ambient temperature for twentyfour hours.

The percentage retardation caused by the added inhibitor was calculated from the formula:

Percentage retardation= where Lu is the rate of weight lossof a piece of metal during pickling in an uninhibited bath and L1 is the rate of loss of weight from apiece of .the same metal under.- going pickling in an inhibited bath.

Table 1 Percentage Percentage Test No. Inhibitor Added Iodine Retarda- Gontent tion 1 0.002% I: 0.002 33 2 0.1% of 2% tincture." 0.002 57 The synergistic efiect obtained from mixing iodine and ethanol is obvious from the figures in the fourth column of Table 1.

Example 2.--Tests were run as in Example 1 except that 0.02% of iodine inhibitor was used. This percentage was obtained, 1) by adding 0.02% of I2 directly to the pickling bath; (2) by adding 1% of a 2% commercial tincture of iodine; and (3) by adding 1% of a 2% ethanol tincture made up in the laboratory. Results obtained are summarized in Table 2.

Table 2 Percentage Percentage Test No Inhibitor Added Iodine arde- Oontent tion 0.02 It 0. 02 1% ofa 2% Com. Tincture.. 0.02 95 1% of 2% Lab. Tincture 0. 02 90 The reciprocal synergistic influence of iodine and ethanol upon each other is again evident from the fourth column of the table.

Example 3.-The tests of Examples 1 and 2 were repeated utilizing, however, a concentration of 0.10% iodine. This concentration was obtained (1) by adding 0.10% I2 directly to the pickling bath and again (2) by adding 5% of a 2% commercial tincture of iodine to the bath. Results obtained are shown in Table 3.

Table 3 Percentage Percentage Test No. Inhibitor Added Iodine etarda- Content tion 6 0.10% 12 0. 1 7 5% ofa 2% Com. Tincture.. 0. 1 91 non-oxidizing pickling acid and water, said composition carrying dissolved therei'na sufiicient amount of a tincture of iodine to provide iodine to the extent of between about 0.002% and about 0.1% by weight of said composition.

2. A composition of matter for pickling ferrous metals consisting essentially of an aqueous solution of sulfuric acid carrying dissolved therein a sufiicient amount of a tincture of iodine to provide iodine to the extentof between about 0.002% and about 0.1% by weight of said solution.

3. The method of inhibiting corrosion of ferrous metal articles in a non-oxidizing acid pickling bath which comprises supplying to said bath a small but effective quantity of tincture of iodine.

4. A composition of matter consisting essentially of a non-oxidizing acid bath for pickling metals, said bath carrying dissolved therein a corrosion inhibiting agent comprising approximately ten parts of ethanol and one part of iodine, said inhibitor constituting not more than 5% by weight of said bath.

References Cited in the file of this patent UNITED STATES PATENTS 453,129 Reeser May 26, 1891 1,809,041 Jenkins et a1. June 9, 1931 2,399,134 Miller et al. Apr. 23, 1946 2,477,181 Holman July 26, 1949 OTHER REFERENCES Pharmaceutical Formulas, vol. 1, 11th ed., The Chemist and Druggist, 1944, London, page 629. 

2. A COMPOSITION OF MATTER PICKING FERROUS METALS CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF SULFURIC ACID CARRYING DISSOLVED THEREIN A SUFFICIENT AMOUNT OF A TINCTURE OF IODINE TO PROVIDE IODINE TO THE EXTENT OF BETWEEN ABOUT 0.002% AND ABOUT 0.1% BY WEIGHT OF SAID SOLUTION. 